High turnover of fungal hyphae in incubation experiments

Abstract

Soil biological studies are often conducted on sieved soils without the presence of plants. However, soil fungi build delicate mycelial networks, often symbiotically associated with plant roots (mycorrhizal fungi). We hypothesized that as a result of sieving and incubating without plants, the total fungal biomass decreases. To test this, we conducted three incubation experiments. We expected total and arbuscular mycorrhizal (AM) fungal biomass to be higher in less fertilized soils than in fertilized soils, and thus to decrease more during incubation. Indeed, we found that fungal biomass decreased rapidly in the less fertilized soils. A shift towards thicker hyphae occurred, and the fraction of septate hyphae increased. However, analyses of phospholipid fatty acids (PLFAs) and neutral lipid fatty acids could not clarify which fungal groups were decreasing. We propose that in our soils, there was a fraction of fungal biomass that was sensitive to fertilization and disturbance (sieving, followed by incubation without plants) with a very high turnover (possibly composed of fine hyphae of AM and saprotrophic fungi), and a fraction that was much less vulnerable with a low turnover (composed of saprotrophic fungi and runner hyphae of AMF). Furthermore, PLFAs might not be as sensitive in detecting changes in fungal biomass as previously thought.

Fungal communities are more sensitive indicators to non-extreme soil moisture variations than bacterial communities

“…When a moisture shift occurs, a reduction of the activity of dominant fungi adapted to previous moisture content could result in a reduction in competitive ability against other fungal taxa, which will then be able to dominate the community at the new water content (Allison and Treseder, 2008). The rapid observed shift is quite surprising, but could be explained by rapid hyphal turnover (Staddon et al, 2003De Vries et al, 2009 and the ability of some taxa to grow even in drying periods (Bapiri et al, 2010;Yuste et al, 2011). Therefore, the drought tolerance of fungal communities often claimed in studies could be explained not only by facilitated nutrient access through hyphal networks, but also by a rapid turnover of populations conferring high plasticity to the community.…”

Extensive Management Promotes Plant and Microbial Nitrogen Retention in Temperate Grassland

“…In contrast, bacterial PLFA and bacterial biomass, as measured by microscopy, both tended to be greater in extensive grasslands, and by the same magnitude (25%). An explanation for the discrepancy between fungal PLFA and microscopic counts of fungal hyphae could be that a large part of hyphae visible through a microscope might be inactive or dead [54], although the assumption that PLFAs degrade more rapidly than cell walls, and thus represent active biomass more accurately than microscopy, has been challenged [55]. Although all of our samples were treated and stored in a similar way, storage might have resulted in differences in decay of fungal hyphae and PLFAs, although this is hard to judge given that very little is known about the impacts of pre-treatment of soil samples on these methods [55], [56].…”

In situ gross nitrogen transformations differ between temperate deciduous and coniferous forest soils

“…Our results also indicate that heterotrophic nitrification of organic N is an important process of NO 3 -production in temperate acid forest soils. Heterotrophic nitrification is predominantly carried out by fungi, including ectomycorrhizae (Killham 1990) whose mycelium networks are fragmented by soil sieving (Bengtsson et al 2003;de Vries et al 2009) or delimiting soil cores. In this respect, the present gross N rates determined in undisrupted soils are more representative for the actual gross N dynamics.…”